1. Field of the Invention
The present invention relates to a camera to which a lens unit is removably secured.
2. Description of the Related Art
In recent years, video apparatuses, such as video cameras, have made remarkable advances, and more development effort has been directed to realizing video apparatuses having more functions and higher performance.
In such a situation, to increase the number of functions to be incorporated into a video camera, a high-magnification zoom lens has been employed as optical zoom, and an electronic-zoom function for enlarging a picked-up image by electronic image processing through signal processing on a camera-body side has been realized as electronic zoom.
By combining the optical zoom and the electronic zoom, it is possible to obtain a magnification equivalent to the product of the magnification of the optical zoom and that of the electronic zoom, so that it is possible to realize a zooming operation of higher magnification.
In addition, as one method of realizing more functions and higher image quality, it has been proposed to use an interchangeable lens system as a lens system for a video camera, so that it has been become possible to realize a video camera capable of coping with any photographic condition. In the interchangeable lens system, the combination of the optical zoom and the electronic zoom makes it possible to select lenses so that the main characteristics of the respective lenses can be utilized as effectively as possible. Such combination is, therefore, extremely effective in coping with more photographic conditions.
In the above-described combination of the optical zoom and the electronic zoom, in general, zooming is performed by using the optical zoom which does not cause a degradation in image quality, within the range of magnifications which can normally be covered by the optical zoom, and after the optical zoom reaches its telephoto end, the optical zoom is switched to the electronic zoom so that an image is electronically enlarged.
However, when the optical zoom reaches the telephoto end and is switched to the electronic zoom, if the magnification variation rate of the image differs between the optical zoom and the electronic zoom, the magnification variation rate of the image changes sharply, so that the image may undergo an unnatural and abrupt change.
As is known, in an integrated-type video camera in which its lens unit and its camera body are inseparably fixed to each other, even if the magnification variation rate differs between the optical zoom and the electronic zoom, the magnification variation rate changes in one particular manner at all times. In contrast, in an interchangeable-lens type video camera in which its lens unit is interchangeably secured to its camera body and plural kinds of lens units can be combined with the camera body, the plural kinds of lens units normally are respectively provided with different magnification varying lenses each having not only a different moving speed but also a magnification variation rate of a different variation pattern. Such an interchangeable-lens type video camera has the disadvantage that the transition from the optical zoom to the electronic zoom (or vice versa) is not smoothly performed and, in addition, the manner of such transition differs among the kinds of lens units used.
It is, therefore, a first object of the present invention to provide a camera system for an interchangeable-lens type camera, which is capable of executing smooth control whatever kind of lens unit is secured to a camera body.
A second object of the present invention is to provide an image pickup apparatus, a lens unit and a camera each of which is capable of effecting a smooth transition between optical zoom and electronic zoom without causing an unnatural or abrupt change in an image, as well as an interchangeable lens system in which whatever kind of lens unit is secured to a camera body, it is possible to effect a smooth transition between optical zoom and electronic zoom without causing an abrupt change in an image.
To achieve the above objects, according to one aspect of the present invention, there is provided a lens unit which is removably secured to a camera body and which comprises a magnification varying lens for performing a magnification varying operation, communication means for communicating data with the camera body, and control means for transmitting information relative to an amount of variation per unit time of a focal length of the magnification varying lens to the camera body via the communication means.
According to another aspect of the present invention, there is provided a lens unit in which the communication means is arranged to transmit to the camera body the information relative to the amount of variation per unit time of the focal length of the magnification varying lens and information relative to a position of the magnification varying lens.
According to another aspect of the present invention, there is provided a lens unit in which information indicating whether the magnification varying lens is located at its telephoto end is transmitted as the information relative to the position of the magnification varying lens.
According to another aspect of the present invention, there is provided a lens unit in which the magnification varying lens is capable of operating at a plurality of speeds, and the information relative to the amount of variation per unit time of the focal length of the magnification varying lens includes a plurality of pieces of information which respectively correspond to the plurality of speeds of the magnification varying lens.
According to another aspect of the present invention, there is provided a camera to which a lens unit is removably secured and which comprises image pickup means, electronic-zoom means for electrically varying a magnification of an image signal outputted from the image pickup means, communication means for receiving from the lens unit information relative to an amount of variation per unit time of a focal length of a magnification varying lens, and control means for controlling a magnification variation rate of the electronic-zoom means on the basis of the information.
According to another aspect of the present invention, there is provided a camera in which the control means controls the magnification variation rate of the electronic-zoom means on the basis of the information relative to the amount of variation per unit time of the focal length of the magnification varying lens and the information relative to the position of the magnification varying lens.
According to another aspect of the present invention, there is provided a camera in which the information relative to the position of the magnification varying lens is information indicating whether the magnification varying lens is located at its telephoto end.
According to another aspect of the present invention, there is provided a camera in which the magnification varying lens is capable of operating at a plurality of speeds, and the information relative to the amount of variation per unit time of the focal length of the magnification varying lens includes a plurality of pieces of information which respectively correspond to the plurality of speeds of the magnification varying lens.
According to another aspect of the present invention, there is provided a camera which comprises a magnification varying lens for performing a magnification varying operation, image pickup means, electronic-zoom means for electrically varying a magnification of an image signal outputted from the image pickup means, and control means for controlling a magnification variation rate of the electronic-zoom means on the basis of information relative to an amount of variation per unit time of a focal length of the magnification varying lens.
According to another aspect of the present invention, there is provided a camera in which the control means controls the magnification variation rate of the electronic-zoom means on the basis of the information relative to the amount of variation per unit time of the focal length of the magnification varying lens and information relative to a position of the magnification varying lens.
According to another aspect of the present invention, there is provided a camera in which the information relative to the position of the magnification varying lens is information indicating whether the magnification varying lens is located at its telephoto end.
According to another aspect of the present invention, there is provided a camera in which the magnification varying lens is capable of operating at a plurality of speeds, and the information relative to the amount of variation per unit time of the focal length of the magnification varying lens includes a plurality of pieces of information which respectively correspond to the plurality of speeds of the magnification varying lens.
According to another aspect of the present invention, there is provided an image pickup apparatus which comprises a lens unit including a magnification varying lens capable of varying its focal length at a plurality of speeds, a camera body to which the lens unit is secured and which includes an image pickup element and a signal processing circuit, selection means for selecting either one of a first communication mode for mainly communicating information peculiar to the lens unit and a second communication mode for mainly communicating information indicative of control and a state of the lens unit, and control means provided in the a camera body and arranged to obtain, if the first communication mode is selected, information relative to amounts of variations per unit time of a focal length of the magnification varying lens of the lens unit which respectively correspond to the plurality of speeds of the magnification varying lens.
According to another aspect of the present invention, there is provided an image pickup apparatus in which the control means is arranged to obtain information relative to a position of the magnification varying lens if the second communication mode is selected.
According to another aspect of the present invention, there is provided an image pickup apparatus in which the information relative to the position of the magnification varying lens is information indicating whether the magnification varying lens is located at its telephoto end.
Another object of the present invention is to provide an interchangeable-lens type camera having improved AF performance, particularly an interchangeable-lens type camera which is capable of achieving optimum AF performance at all times irrespective of the kind of lens unit used.
Another object of the present invention is to improve the AF characteristics of an automatic focus adjusting operation to be carried out during execution of an optical-zoom operation and an electronic-zoom operation.
The above and other objects, features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments of the present invention, taken in conjunction with the accompanying drawings.